The annular cavity that is formed downstream of the rotor or impellor of a centrifugal compressor in a turbomachine must be ventilated to take away the heat energy generated by the impellor. This ventilation is usually provided by taking air from the output of the compressor, at the junction with the inlet of an annular diffuser that supplies a combustion chamber.
This ventilation air that already has a relatively high temperature, heats up through viscous friction on the downstream face of the impellor while running from the outside to the inside in the downstream cavity of the impellor, the air becoming hotter as it comes closer to the axis of rotation of the impellor. This hot air may, by convection, raise the temperature of the impellor, and in particular its radially internal portion where the mechanical stresses are the highest in operation, which causes a risk of damage to the impellor by material creep.